Entities do not simply precede their relations. What appears stable—a concept, institution, body, city, discipline or climate regime—is the provisional result of repeated acts of distinction, inscription, constraint, maintenance and support. CategoryEmergence names the process by which these relational arrangements harden sufficiently to appear self-evident. Categories are produced stabilisations rather than natural containers. A boundary repeated in law, language, architecture and habit may eventually look prior to the practices that created it. Form is therefore the temporary durability of relation. This does not imply that reality is infinitely malleable. Material resistance, historical accumulation, unequal power and institutional investment give some arrangements immense persistence. Yet even durable categories remain composed, and what has been composed can in principle be recomposed. The concept redirects attention from asking what an entity essentially is toward tracing how it acquired continuity, which supports maintain it and where instability still survives. Reality becomes plastic precisely because stabilisation is real: transformation must encounter and reorganise the relations through which form has learned to endure.